1. Field of Invention
The present invention relates generally to a method and apparatus for affecting a subject's health or condition by using information regarding the sympathetic and/or parasympathetic branches of the subject's autonomic nervous system to apply and/or modulate stimuli to the subject. The present invention also relates to a method and apparatus for affecting the autonomic nervous system, wherein stimuli is applied in coordination with cyclical activities of the subject's body.
2. Background Art
The autonomic nervous system (ANS) and its role in health and pathology is a field of medicine that has been explored and written about at great length. There are also several prior art methods and devices that use the concept of applying sensory stimuli to a subject's body to affect the subject's health or condition.
I. Application of Stimuli to Affect the Body
The prior art includes methods and devices for applying stimuli to a patient's body. For example, U.S. Pat. No. 5,577,990 to Widjaja et al. discloses a device that directs light and sound toward a patient, apparently eliciting a relaxation response from the patient. It is also known in the art to combine stimuli with feedback from the body. For example, U.S. Pat. No. 5,562,719 to Lopez-Claros discloses a method and apparatus for treating disorders such as Seasonal Affective Disorder by preferentially directing light therapy to the non-dominant hemisphere of the brain. In addition, U.S. Pat. No. 4,289,121 to Kupriyanovich discloses a method and device for controlling the functional state of the central nervous system using audio and light signals applied according to the body's biorhythms that correspond to a stable state of the central nervous system. This reference describes modulating frequencies depending on the electroencephalogram (EEG), electrocardiogram (ECG), or the measured respiration rate of the patient, wherein the amplitude or rhythmic signals correspond to the volume of sound and brightness of light. Kupriyanovich also suggests that the device include a feedback system to automatically vary the illumination in response to certain changes in the patient's vital signs, including the patient's pulse rate, temperature, and respiratory rate. A patient's vital signs, however, do not provide complete information about the autonomic nervous system. The same vital sign reading for one patient may represent different levels of sympathetic and parasympathetic activity. Therefore, the complexity or the various dimensions of the autonomic nervous system activity is not fully reflected in a patient's vital sign measurements or in the patient's biorhythms.
In addition, in the prior art methods and devices, stimuli which generally affect the sympathetic branch differently than the parasympathetic branch, are applied without regard to the autonomic nervous system balance and activity. For example, U.S. Pat. No. 5,076,281 to Gavish discloses a biorhythm modulator, which produces music-like sound pattern signals based on a patient's biorhythmic activity. Although Gavish notes that certain activities of the body are associated with the sympathetic nervous system, the rhythm of the sound synthesized patterns are based simply on a patient's monitored respiration rate, and not on separate analyses of the sympathetic and parasympathetic branches of the autonomic nervous system.
The prior art also includes stimulation treatments and biofeedback treatments that involve the patient's cognitive awareness and involvement in the treatment. These treatments are also known to include adjustment of the stimuli through trial and error. In the Kupriyanovich reference described above, the patient chooses the initial light and audio signals. However, a patient's subjective feelings do not accurately reflect the complex interactions of the patient's autonomic nervous system.
It is known that, generally, colors ranging from green to blue or violet are calming colors, and that these colors have the effect of stimulating the parasympathetic branch. It is also known that, generally, colors ranging from red to yellow are rousing colors, and that these colors have the effect of stimulating the sympathetic branch. Hospitals tend to incorporate greens and blues in their interior color scheme in order to calm and soothe patients, whereas fast food restaurants are typically red, yellow, and orange in order to move customers in and out of the restaurants quickly. In addition, it is known that increasing the brightness or intensity of a color increases its stimulatory effect.
It is also known that, generally, sounds having a pitch below 500 cycles or Hz tend to have a calming effect, whereas sounds having a pitch above 500 cycles tend to have a rousing effect. In addition, it is known that the louder the sound, the greater the stimulation.
As is apparent from the discussion above, known methods or devices generally do not provide for treatment of a patient based on the full range of information which can be ascertained from the condition of the autonomic nervous system. For example, prior art treatment methods or devices generally do not take advantage of independent or separate analyses of the sympathetic and parasympathetic branches of the autonomic nervous system.
II. The Autonomic Nervous System and Heart Rate Variability
A. Nervous System
The nervous system comprises the central nervous system and the peripheral nervous system. The central nervous system comprises the brain and spinal cord, and the peripheral nervous system comprises a network of nerves that connects the brain and spinal cord to the rest of the body.
The brain, which is the site of cognitive awareness and the control center for the rest of the body, comprises the cerebrum, the brain stem, and the cerebellum. The brain coordinates the ability to move, touch, taste, smell, hear, and see. The cerebrum regulates a variety of voluntary activities of the body, including speech, thought, planning, and initiating communication or action.
A variety of critical body functions are automatically regulated by the brain stein. These functions include adjusting posture, regulating breathing, swallowing, and heart rate, controlling the rate at which the body burns food, and increasing alertness when needed. The autonomic nervous system is a part of the peripheral nervous system and comprises the nerves that communicate between the brain stem and the body's internal organs.
The autonomic nervous system comprises the sympathetic and parasympathetic branches or systems, and it functions below the conscious level through complex interactions between its two branches to respond quickly and continuously to perturbations that threaten the stability of the body's internal environment.
Responses to sympathetic and parasympathetic stimulation are frequently antagonistic. For example, they have opposing or antagonistic effects on heart rate. Whereas stimulation of the sympathetic branch increases heart rate, stimulation of the parasympathetic branch decreases heart rate. In addition, the body's response to activity in one branch depends on the level of activity in the other branch.
A useful, albeit simplistic, analogy for the parasympathetic and sympathetic branches is that the sympathetic branch functions as the body's gas pedal and the parasympathetic branch functions as the body's brakes. Sympathetic and parasympathetic activity make up a complex, dynamic system that is continuously adjusting to changing conditions in the body and in the outside environment. The autonomic nervous system strives to optimize activity in each branch and to balance the two branches at every passing moment, depending on both internal and external conditions.
B. Heart Rate
Normal rhythmic contractions of the heart occur because of spontaneous electrical pacemaker activity of cells in the sinoatrial (SA) node. The heart rate, i.e., the time interval between heartbeats, is determined by how long it takes the membranes of these pacemaker cells to spontaneously depolarize to the threshold level. The heart beats at a spontaneous or intrinsic rate, which is approximately 100 beats per minute, in the absence of outside influences. Outside influences are required to increase or decrease the heart rate from its intrinsic rate.
The two most important outside influences on heart rate come from the autonomic nervous system. Fibers from both the sympathetic branch and parasympathetic branch of the autonomic nervous system terminate on cells in the SA node and both can modify the intrinsic heart rate. Activating the cardiac sympathetic nerves increases cardiac sympathetic tone, thereby increasing heart rate. Increasing cardiac parasympathetic tone, on the other hand, slows the heart rate. Both sympathetic and parasympathetic nerves influence heart rate by altering the course of spontaneous depolarization of the resting potential in SA pacemaker cells.
C. Heart Rate Variability (HRV)
Heart rate variability is the amount of heart rate fluctuation around a mean heart rate. Such fluctuations reflect oscillations in sympathetic-parasympathetic balance associated with a variety of factors, including respiration, baroreceptor reflexes, vasomotor control, and thermoregulatory processes. The main periodic fluctuations found are respiratory sinus arrhythmia and baroreflex-related and thermoregulation-related heart rate variability.
Heart rate variability is demonstrated by every normal person's heart, regardless of that person's state of health and regardless of the presence of stress or disturbances. Even a sleeping person displays heart rate variability. Each person has a measurable baseline heart rate variability even in the absence of external stressors, such as traffic, screaming babies, and looming deadlines.
Heart rate variability can be used as a mirror of the cardiorespiratory control system, and it is a valuable tool to investigate the sympathetic and parasympathetic function of the autonomic nervous system. Heart rate variability provides information about sympathetic-parasympathetic interplay and balance, which includes other valuable information about the nervous system, including, for example, the risk for sudden cardiac death in patients after myocardial infarction.
Heart rate variability measurements are easy to perform, are noninvasive, and are easily and accurately reproducible. In addition, heart rate variability has been found to be largely unaffected by placebos.
Heart rate variability can be influenced by physiologic and maturational factors. Maturation of the autonomic nervous system results in an increase in heart rate variability with gestational age and during early post-natal life. Heart rate variability decreases with age, and this decline begins in childhood. In addition, heart rate variability is influenced by provocation and physical disorders.